Rate of twin births increased in pregnancies with higher BMI

The rate of twin deliveries increased with increasing body mass index (BMI), and part of this association was explained by higher use of assisted reproductive technology (ART), according to a study published online Jan. 9 in JAMA Network Open.

Jeffrey N. Bone, from the University of British Columbia in Vancouver, Canada, and colleagues examined the association between BMI and twin birth and the role of ART as a potential mediator in this association. The analysis included 392,046 deliveries (gestational age of ≥20 weeks) with complete data identified from the British Columbia Perinatal Database Registry (2008 to 2020).

The researchers found that when adjusting for other covariates, women with underweight had relatively fewer twins compared with women with normal BMI (adjusted risk ratio [aRR], 0.84), while women with overweight, class I obesity, class II obesity, and class III obesity had higher rates (aRRs, 1.14, 1.16, 1.17, 1.41, respectively).

Additionally, the proportion of women who conceived by ART increased with increasing BMI. ART was associated with a substantially higher rate of twin delivery (aRR, 11.80) and explained about one-quarter of the association between obesity class I and II and twin delivery (e.g., obesity class I, 23 percent mediated).

"We found a relatively small excess of twin deliveries in women who had overweight and obesity prior to pregnancy compared with women with normal BMI," the authors write.

One author disclosed ties to the pharmaceutical industry.

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